The increasing popularity of elaborate Quality-of-Service (QoS) frameworks such as Integrated Services [see reference 1 listed in the attached Appendix] and Differentiated Services [2] puts emphasis on packet schedulers that allow flexible bandwidth management. Several existing packet schedulers offer excellent worst-case delay performance in addition to providing accurate bandwidth guarantees [3, 4, 5, 6, 7, 8], but their cost is substantial [6, 7, 8]. In IP networks, the enforcement of tight delay guarantees is still rather secondary to the low-cost provision of robust bandwidth guarantees. For this reason, the industry is showing considerable interest in Weighted Round Robin (WRR) schedulers [9, 10, 11], which do not necessarily achieve tight delay bounds, but do provide robust bandwidth guarantees with minimal complexity. Different instances of these schedulers have appeared in literature; well-known examples are the Deficit Round Robin (DRR) algorithm [10] and the Surplus Round Robin (SRR) algorithm [11].
The aforementioned instances of WRR schedulers successfully differentiate the bandwidth guarantees of heterogeneous data packet flows. However, with respect to the form in which they are currently defined, they are not sufficient to satisfy all the bandwidth requirements of emerging Quality-of-Service frameworks. Typically, flexible bandwidth management at the network nodes requires the deployment of hierarchical scheduling structures, where bandwidth can be allocated not only to individual flows, but also to aggregations of those flows. With existing WRR schedulers, the superimposition of a hierarchical structure for achieving bandwidth segregation compromises the simplicity of the basic scheduler.
What is desired in the art of scheduling for data packet networks is an improved scheduler apparatus that achieves hierarchical bandwidth segregation without compromising the simplicity of the basic scheduler.